Those are some of the basic letters... Like alphabet and some combinations that have different sounds. I don't advise learning them except to recognise sound
So, whenever syllables are written in Korean there are things called "Final Consonants" which means that the character ends with a one of the 14 consonants. When certain characters are used at the end of a syllable, they'll have the same phonetic sound instead of having different phonetic sounds (which is the case when they're not used as a final consonant). For example, when ㄱ, ㅋ, and ㄱㄱ are used as a final constant, they will make the [k']/[euk] sound instead of making the [g'], [k'], and [kk] sounds, respectively. Hope this helps!
Those are korean letters, on the first row, the sequence of the characters from bottom to top will be: G, N, D, ㄹR,ㅁM,ㅂB,ㅇ(silent when on the front or NG if at the end). If you search keywords about learning hangul, you can definitely find some good videos that will crash course you about it. Good luck!